Vacuum type circuit interrupter with improved vapor-condensing shielding



May 25, 1965 c. H. 'rn-Us 3,185,800

VACUUM TYPE CIRCUIT INTERRUPTER WITH IMPROVED VAPOR-CONDENSING'SHIELDING Filed Feb. 18, 1965 CHARLES H. 77H16,

5V Lf-cm ATTORNEY.

United States Patent 3,185,800 VACUUM TYPE CIRCUIT INTERRUPTER WITHIMPROVED VAPOR-CONDENSING SHIELDING Charles H. Titus, Newtown Square,Pa., assignor to General Electric Company, a corporation of New YorkFiled Feb. 18, 1963, Ser. No. 259,298 Claims. (Cl. 200-144) Thisinvention relates to a circuit interrupter of the vacuum type and, moreparticularly, to improved shielding structure for protecting theinsulation of such an interrupter from being impaired by thecondensation thereon of arc-generated metallic vapors.

It is customary to protect the tubular insulating housing of a vacuumcircuit interrupter from such vapor condensation by providing some formof shielding, preferably of metal, located between the insulatinghousing and the arcinggap of the interrupter. This shielding acts in aknown manner to intercept and condense arc-generated vapors before rtheycan reach the insulating housing, thus preventing the vapors fromcondensing on and coating the insulation with metal particles.

In order to prevent any arc present across the arcing gap fromtransferring to the metallic shielding, it is desirable to space theshielding as far away as possible from the arcing gap. But the amount ofspacing available in an interrupter of a given size is limited, and thusthe spacing between the arcing gap and the shielding must be limited. Inview of this limited spacing, there is a remote possibility underunusual .interrupting conditions that :the arc will strike theshielding.

An object of the present invention is to construct the shielding in sucha manner that in the remote event that the arc does strike theshielding, it Will be divided into three series-related arclets.

Another object is to construct the shielding in such a manner as tominimize the chances that a small arc or spark across a gap to theshielding will result in the development of a full scale power arcinvolving the shielding and shorting out the main arcing gap between thecontacts.

Another object is to construct the shielding in such a manner that themetallic particles emitted from the arcing gap will be forced to make atleast two bounces before they can reach the insulating housing.

In carrying out the invention in one form, I provide an evacuatedenvelope comprising a tubular portion of insulating material and a pairof relatively movable contacts disposed within the envelope in alocation surrounded by the tubular insulating portion. The contacts areseparable to form an arcing gap therebetween across which electric arcsare adapted to be developed. Internally of the tubular insulatingportion a pair of tubular metallic shields are disposed for protectingthe tubular insulating portion from arc-generated vapors. These tubularshields are spaced from each other in a direction longitudinal of thetubular insulating portion with an annular gap between adjacent ends ofthe shields. This annular gap surrounds the arcing gap and is locatedgenerally in alignment with the arcing gap, considered in a directionlongitudinal of the tubular insulating portion. These shields aremounted in electrically isolated relationship` with respect to eachother and with respect to the contacts. A third tubular shield surroundsthe annular gap and the adjacent ends of the first two shields. Thethird shield is mounted in radially spaced relationship 4relative to theiirst two shields and is electrically isolated relative to these twoshields and relative to the contacts. The three shields are suiiicientlyspaced radially outward from ythe contacts that arcs established betweenthe contacts do not normally engage the shields.

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For a better understanding of the invention, reference may be had to thefollowing description taken in conjunction with the accompanyingdrawings, wherein:

FIG. l is a sectional view through a vacuum interrupter embodying oneform of my invention,

FIG. 2 is an enlarged view of a portion of the interruptor of FIG. l.

Referring now to FIG. l, the vacuum type circuit interrupter showntherein comprises a highly evacuated envelope 1G. This envelope 1i)comprises a tubular insulating housing 12 and a pair of metallic endcaps 14 and 16 located at opposite ends of the insulating housing 12.The end caps 14 and 16 are joined to the insulating housing 12 by meansof vacuum-tight seals 18.

The insulating housing 12 comprises a plurality of short tubularsections 2t), 21, 22 and 23, each of a suitable insulating material suchas glass. These tubular insulating sections are disposed in colinearrelationship and are joined together by metallic tubes 24 formingkvacuum-tight glass-to-metal seals between the insulating sections.

Disposed Within the envelope 10 are two relatively movable contacts 26and 28, shown in their fully separated position. The upper contact is astationary contact, and the lower contact 28 is a movable contact. The

yupper contact 26 is suitably brazed to the lower end of a conductivesupporting rod 30, which is integrally joined at its upper end to themetallic end plate 16. The lower contact is suitably brazed to the upperend of ka conductive operating rod 32, which is vertically movable toeffect opening and closing of the interrupter.

For permitting vertical motion of the operating rod 32 Withoutimpairment of the vacuum inside the envelope 10, a suitable bellows 33is provided about the operating rod. This bellows 33 is joined in sealedrelationship at its respective opposite ends to the end pla-te 16 andthe operating rod 32. A cup-shaped shield 35 surrounds the bellows 33and protects it from being bombarded by arcing products, as will soonappear more clearly.

The interruptor can be closed by driving the lower contact 28 upwardlyinto its dotted line position 29, where it engages the upper contact 26.When the contacts are so engaged, current can flow between opposite endsof the interrupter via the parts 30, 26, 28, and 32.

Circuit interruption is eiiected by driving the contact 28 downwardlyfrom its dotted line position to its solidk line position by suitableoperating means (not shown). This downward motion of Contact 2Sestablishes an arc between the two contacts across an arcing gap 34located between the contacts. Assuming an alternating current circuit,this are persists until about the time a natural current zero isreached, at which .time it vanishes and is thereafter prevented fromreigniting by the high dielectric strength of the vacuum. A typical arcthat is formed during the circuit interrupting operation is illustratedat 36.

The arc that is developed during each circuit interrupting operationvaporizes some of the contact or electrode material, and the resultingmetallic vapors are ejected radiallyoutward from the arcing gap 34 inall directions.

, For protecting the insulating housing 12 from these metallic vapors, Iprovide a series of tubular shields 40, 42, 44, 46, and 48. Theseshields, which are of metal, cooperate with the metallic end plates 14and 16 and the bellows shiel-d 35 to intercept substantially all of thearc-generated vapors before they can reach the insulating housing 12. Inthis regard, the metallic particles that are emitted from the arcing gaptravel in essentially straight line paths from the region of the arcinggap. All of the straight line paths intersect either one of thesemetallic shields or the metallic end plates 14 or 16. Most of themetallic particles are condensed on this first collision with themetallic parts,

but a small percentage will bounce oit, being free to leave the surfacein any direction but still traveling in a generally straight line path.Essentially all of these rebound paths are intersected by another shieldor by the end plates T4 or 16, thus giving the shield or end plateanother opportunity to condense the metallic particle. No signicantpercentage of the metallic particles appears to bounce oft thecondensing surface after the second collision. Thus, no signiticantnumber of the particles reaches the insulating housing.

The tubular shields 4t) and 44 are disposed in generally alignedrelationship and are spaced apart in a longitudinal direction to definean annular gap 5t) therebetween. The annular gap Sti surrounds thearcing gap 34 and is substantially aligned with the arcing gap 34 in adirection longitudinal of the tubular insulating housing l2.

The lower shield 4@ is mounted on a radially extending annular disc 51that is joined at its outer periphery to one of the metallic tubes 24.At its inner periphery this supporting disc 5l is suitably joined to thetubular shield 40. A similar disc 53 supports the upper tubular shield44. Since the shields dit) and @d are physically spaced apart by meansof the gap Sti and are each mounted on the insulating housing l2 inspaced-apart relationship, it will be apparent that they areelectrically isolated from each other. It should also be noted that thelower shield 4@ is electrically isolated from the lower end cap by meansof a vacuum gap 56 located between the end cap and the shield 40 andalso by means of the lower insulating section Ztl. Similiarly, the uppershield die is electrically isolated vfrom the upper end cap by means ofan interposed vacuum gap 58 and tubular insulating section 23.

Surrounding the annular gap 5@ and the adjacent ends of tubular shieldsitl and 44 is the third tubular shield 42. This tubular shield ft2 isradially spaced from the tubular shields all and le by means of annulargaps 52 and 54, respectively. The third tubular shield 42 is supportedon the tubular insulating housing l2 by means of a metallic disc 57.This disc 57 is suitably joined at its outer periphery to the centralmetallic tube 24E- and at its inner periphery to shield 4?..

The shields ttl and i4 are spaced a suliicient distance radially outwardfrom the contacts 26 and 2t; normally to prevent any arc between thecontacts from striking the shields 46 and 4d. Even though the arc mightbe located at the radially outermost periphery of the contacts 26 and 28and may be bowing outwardly as indicated at 36, it still will notnormally strike the shields 4t) and 44. The gap 62 between the contact26 and shield 44, and the gap 64E. between the contact 28 and the shielditl are long enough normally to prevent the outwardly-bowing arc fromstriking the shields. Since the shield l2 is located radially outwardlyof the shields ttl and 44, there is even less likelihood of the arcstriking this shield 412.

Most of the vapors emitted from the arcing gap 3ft are intercepted andcondensed by one of the main shields llt), 42 or 44. Sonie of thesevapors pass radially outward through the annular gap 50, but they areintercepted and condensed by the central shield 42; before they canreach the insulating housing l2. The aligned relationship of the centralshield 42 with the gap 5t) facilitates elective interception of thevapors passing through the gap Sil.

There is a slight possibility that under unusual interrupting conditionthe arc between contacts 26 and Z8 may bow outwardly enough to strikethe shields 40 and de. This would result in a division of the arc intothree seriesrelated arclets across the gaps 62k, 50 and d4,respectively. Such a division of the arc would help the interrupterrecover its dielectric strength after current zero, thus facilitatinginterruption, particularly as compared to the case where one or even twoarcs to the shielding constitute the current path between the contacts.

For reasons which are no yet clearly understood, it sometimes happensthat immediately after interruption there is a transient reduction indielectric strength across asco one or more of the gaps in theinterruptor. If a spark should occur across one of these gaps duringthis interval of reduced dielectric strength, it is important that thisspark not develop into a full-scale power arc, particularly a power arcinvolving the shielding. I have minimized the chances that such a sparkwill develop into a full-scale power arc by the above-described divisionof the shielding into the three major portions 40, 42 and 44, eachelectrically isolated from the other and from the end plates 14 and leand the contacts 26 and 28.

Thus, if a spark should occur across the gap 58 between the upper endplate T6 and the upper main shield 44, there are still gaps 5t) and 56available to isolate the shield 44tfrom the other end plate 14. Thisisolation prevents power follow current from flowing and converting thespark into a full-scale power arc. Even if sparks should simultaneouslydevelop across gaps 56 and 58, the gap 5t) between the shields 4t) and44 is still available to maintain the electrical isolation between thetwo end caps 14 and lo. This gap 56 is of such a length that it normallyhas suiiicient dielectric strength to withstand without breakdown themaximum voltages that are developed between the end plates 14 and 16.The gaps 52 and 54, taken together, also have sufiicient dielectricstrength to withstand such maximum voltages, thus preventing a breakdownacross these gaps, which could short out the gap 50.

As an additional precaution against the gap 50 breaking down under theseconditions, I make the gap 50 longer than the gap 34 between thecontacts 26 and 28. Thus, the inter-contact gap 341 is more likely tobreak down than the gap Se in response to full voltage being appliedacross the two gaps 34 and 50 simultaneously. This is desirable becausean arc across the inter-contact gap 34 can be handled much more easilythan an arc across the gap 50. In this respect, the contacts 26 and 28are of a material especially adapted for arcing duty, and also theshielding structure is more capable of protecting the insulating housingl2 trom arcing vapors generated across the nter-contact gap 34 ratherthan at other locations in the interrupter.

If in spite of all the precautions taken against a breakdown betweenshields atl and d4, a breakdown should, for some remote reason, stilloccur, then I prefer that it occur across the gap Sil in preference toseries-related breakdowns Iacross the gaps 52 and 54. One of my reasonsfor this preference is that an arc present across the gap 5@ can beforced to bow radially inward toward the contacts 26, 2S; thus providingsome opportunity for a transrer of the arc to the contacts 26, 28. Suchan arc is depicted at 73 in FIG. 2. The radially-inwardly bowingconfiguration ot the arc results from the presence of the curls '76) andil at the adjacent end of the shields 40 and 44. As shown in FIG. 2,these curls would force current flowing to an arc terminal on the curlto follow a path L through the shield that extends radially inwardly tothe arc terminal, thus resulting in a radially inwardly bowingconliguration for the current path L.

Another reason for preferring the gap 50 to the gaps 52 and S4 as arclocations is that there is better protection ot the insulating housingfrom arc-generated vapors when the arc is at 5@ rather than at 52 andS4. In this respect, the shield l2 can still provide effective shieldingagainst metallic vapors generated at gap 50 but would be ratherineffective against vapors generated at gaps S2 or 54.

It should be understood that even it the arc or arcs do develop at somelocation other than the intercom-tact gap 34, it is still possible forthe interrupter to extinguish the arcs. The vacuum will still recovermost of its dielectric strength after the iirst natural current zero,thus usually preventing the arcs from reigniting after current zero. Itis greatly preferred, however, that all arcing occur at the arcing gap34 rather than elsewhere in View of the greater suitability of the`contacts for arcing duty and the better shielding that is availablewhen the arcing location is at the arcing gap 34.

As a further example of how my particular shielding reduces the chancesfor a spark to the shielding developing into a full-scale arc, assumesimultaneous sparks across the gaps 62 and 64 between the contacts andthe shielding. Even ythis conditionwould be unlikely to result in anarc. This is the case because there is still the gap 50 available tomaintain isolation between electrically opposed ends of the interrupter.Since -this gap 50 can normally withstand the maximum voltage thatdevelops between the end terminals of the interrupter, it can -prevent afurther breakdown, which would complete a short circuit path around thecontacts 26, 28 and result in arcs across gaps 62, 50 and 64. It shouldbe apparent that if the gap 50 were not present and the shields 40 and44 were electrically interconnected, the simultaneous occurrence ofsparks across the gaps 62 and 64 would have resulted in theestablishment of power arcs.

The manner in which the curls 70 and 71 force an arc toward the mainarcing gap 34 has been described hereinabove. Similar curls are providedat the free ends of al1 of the shields for several reasons. One reasonis to force any arc that might possibly be established at this point ina direction toward the main arcing gap. This will generally reduce thelikelihood that the insulating housing will be coated to anobjectionable extent by arc-generated vapors. Another reason for thecurls is toreduce the electric stress concentrations adjacent the endsof the shield, which stress concentrations would be present if theseends contained exposed sharp corners.

The end shields 46 and 48 are intended to serve several purposes. One isto intercept any metallic particles that are able to avoid the mainshields 40, 44, and 42. Another is to relieve the glass-to-metal sealsfrom undue electric stresses. With respect to the first purpose, the endshields 46 and 48 preferably overlap their adjacent main shields 40 and44 in an axial direction to make any path leading to the insulatinghousing 12 more tortuous, thus increasing the chances for interceptionby one of the shields. With respect lto electric stress relief, theshields 46 and 48, by extending axially inward beyond the end seals,tend to transfer electric stresses from the seals to the inner ends ofthe shields.

Auxiliary shields 76 and 78 can be provided, if desired, to improve theprotection of the insulating sections 21 and 22 against .arc-generatedvapors, particularly when the vapors are being generated at some pointsuch as 50, other than the main arcing gap. These auxiliary shields 76and 78 are likewise of a tubular or annular configuration and help torelieve stresses at the glass-to-metal seals that are locatedimmediately thereadjacent.

The capacit-ances between the shields can be relied upon to provide fora desired distribution of voltage along the insulating housing 12.Preferably, the shields are so proportioned and spaced that thesecapacitances provide for approximately uniform distribution of voltagealong the insulating housing 12 and provide for the shield 42 to be at amidpotential relative to the end plates 14 and 16. A relatively highcapacitance is present between each of the shields 40 and 44 and itsrespective con-tact assembly, so that a relatively low potentialdifference exists between each of these shields and its adjacentcontact.

While I have shown and described particular embodiments of my invention,it will be obvious .to those skilled in the art that various changes andmodifications may be made without departing from my invention in itsbroader aspects, and I, therefore, intend in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedSta-tes is:

1. A vacuum-type electric circuit interrupter comprising:

(a) an evacuated envelope comprising a tubular portion of insulatingmaterial,

(b) a pair of relatively movable contacts disposed within said envelopein a ylocation surrounded by said tubular insulating portion,

(c) said contacts being separable to form an arcing gap therebetweenacross which electric arcs are adapted to be developed,

(d) a pair of tubular metallic shields disposed internally of saidtubular insulating portion for protecting said tubular insulatingportion from arc-generated vapors, y t

(e) said tubular shields being spaced from each other in a directionlongitudinal of said tubular insulating portion with an annular gapbetween adjacent ends of said shields,

(f) said annular gap surrounding said arcing gap and being locatedgenerally in alignment with said arcing gap in a direction longitudinalof said tubular insulating portion,

(g) means for mounting said shields in electrically isolatedrelationship with respect to each other and with respect to saidcontacts,

(lz) a third tubular shield surrounding said annular gap and Itheadjacent ends of said first two shields,

(i) means for mounting said third shield in radiallyspaced relationshiprelative to said first two shields and in electrically isolatedrelationship relative to said first two shields and relative to saidcontacts,

(j) said three tubular shields being sufficiently spaced radiallyoutward from said contacts that arcs established between the contacts donot normally engage said shields.

2. The interrupter of claim l in combination with fourth and fifthtubular shields respectively surrounding the ends of said first andsecond tubular shields that are remote from said annular gap inspaced-apart, electricallyisolated relationship relative to said firstand second shields.

3. The interrupter of claim 1 in combination with fourth and fifthtubular shields respectively surrounding the end of said first andsecond tubular shields that are remote from said annular gap inspaced-apart, electrically-isolated relationship relative to said firstand second shields, and means for electrically connecting said fourthand fifth shields to the respective contacts of said interrupter.

4. The interrupter of claim l in which the adjacent ends of said firstand second shields are provided with radially inwardly extendingportions that force current flowing to an are across said annular gap tofollow a radially inwardly extending path to the arc terminal.

5. A vacuum-type electric circuit interrupter comprising:

(a) an evacuated envelope comprising a tubular portion of insulatingmaterial,

(b) a pair of electrodes of solid material disposed within said envelopein a location surrounded by said tubular insulating portion,

(c) said electrodes having a spaced-apart position defining an arcinggap therebetween across which are developed electric arcs that vaporizematerial of said electrodes,

(d) a pair of tubular metallic shields disposed internally of saidtubular insulating portion for protecting said tubular insulatingportion from said arc-generated vapors,

(e) said tubular shields being spaced from each other in a directionlongitudinal of said tulbular insulating portion with an annular gapbetween adjacent ends of said shields,

(j) said annular gap surrounding said arcing gap and being locatedgenerally in alignment with said arcing gap in a direction longitudinalof said .tubular insulating portion,

(g) means for mounting said shields in electrically isoaisaeao i latedrelationship with respect to each other and with respect to saidelectrodes,

(h) a third tubular shield surrounding said annular gap and the adjacentends of said rst two shields,

(i) means for mounting said third shield in radiallyspaced relationshiprelative to said first two shields and in electrically isolatedrelationship relative to said rst two shields and relative to saidelectrodes,

(j) said three tubular shields being sufficiently spaced radiallyoutward from said electrodes that arcs established between theelectrodes do not normally engage said shields.

, References Cited by the Examiner UNlTED STATES PATENTS 1/41 Steenback313-313 9/44 Beldi 313-239 6/59 Crouch 200-144 3/61 Lee ZOO-144 FOREIGNPATENTS 1/32 France.

BERNARD A. GILHEANY, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

1. A VACUUM-TYPE ELECTRIC CIRCUIT INTERRUPTER COMPRISING: (A) ANEVACUATED ENVELOPE COMPRISING A TUBULAR PORTION OF INSULATING MATERIAL,(B) A PAIR OF RELATIVELY MOVABLE CONTACTS DISPOSED WITHIN SAID ENVELOPEIN A LOCATION SURROUNDED BY SAID TUBULAR INSULATING PORTION, (C) SAIDCONTACTS BEING SEPARABLE TO FORM AN ARCING GAP THEREBETWEEN ACROSS WHICHELECTRIC ARCS ARE ADAPTED TO BE DEVELOPED, (D) A PAIR OF TUBULARMETALLIC SHIELDS DISPOSED INTERNALLY OF SAID TUBULAR INSULATING PORTIONFOR PROTECTING SAID TUBULAR INSULATING PORTION FROM ARC-GENERATEDVAPORS, (E) SAID TUBULAR SHIELDS BEING SPACED FROM EACH OTHER IN ADIRECTION LONGITUDINAL OF SAID TUBULAR INSULATING PORTION WITH ANANNULAR GAP BETWEEN ADJACENT ENDS OF SAID SHIELDS, (F) SAID ANNULAR GAPSURROUNDING SAID ARCING GAP AND BEING LOCATED GENERALLY IN ALIGNMENTWITH SAID ARCING GAP IN A DIRECTION LONGITUDINAL OF SAID TUBULARINSULATING PORTION, (G) MEANS FOR MOUNTING SAID SHIELDS IN ELECTRICALLYISOLATED RELATIONSHIP WITH RESPECT TO EACH OTHER AND WITH RESPECT TOSAID CONTACTS, (H) A THIRD TUBULAR SHIELD SURROUNDING SAID ANNULAR GAPAND THE ADJACENT ENDS OF SAID FIRST TWO SHIELDS, (I) MEANS FOR MOUNTINGSAID THIRD SHIELD IN RADIALLYSPACED RELATIONSHIP RELATIVE TO SAID FIRSTTWO SHIELDS AND IN ELECTRICALLY ISOLATED RELATIONSHIP RELATIVE TO SAIDFIRST TWO SHIELDS AND RELATIVE TO SAID CONTACTS, (J) SAID THREE TUBULARSHIELDS BEING SUFFICIENTLY SPACED RADIALLY OUTWARD FROM SAID CONTACTSTHAT ARCS ESTABLISHED BETWEEN THE CONTACTS DO NOT NORMALLY ENGAGE SAIDSHIELDS.